Undersea optical communication systems include land-based terminals containing transmitters and receivers connected by a cabled-fiber-transmission medium that includes periodically spaced repeaters, which contain optical amplifiers whose purpose is to compensate for the optical attenuation in the cabled fiber. In a bidirectional transmission system each repeater will generally contain two or more optical amplifiers, one for each of the oppositely-directed transmission paths. As the repeaters are usually placed undersea and away from power sources, power must be supplied remotely to the repeaters. The cabled fiber therefore usually contains a cooper conductor to carry electrical power to the repeaters from the terminals. These undersea systems serve to carry optical communication signals (i.e., traffic) between the terminals. The traffic on these systems can consist of voice, data, television, Internet traffic, international telephone traffic, etc. Consequently, the revenue lost when the system is down can be significant. Therefore, these systems must have high reliability and availability.
Recently, ultra-small form factor optical repeaters for undersea use have been developed which have dimensions that are substantially smaller than that of conventional undersea optical repeaters. One example of such a repeater is disclosed in co-pending U.S. application Ser. No. 10/687,547 and U.S. application Ser. No. 10/715,330, which are hereby incorporated by reference in their entirety. One example of the repeater shown in these references has dimensions of only about 7.5 cm×15 cm.
FIG. 1 shows a side view of such an ultra-small form factor repeater. The repeater 100 includes a pressure vessel comprising a cylindrical metallic housing 110 and metallic end caps 1201 and 1202 that are secured to opposing ends of the cylindrical housing 110. The cylindrical housing 110 must withstand high undersea hydrostatic pressures and remain hermetic for at least 25 years. The pressure vessel must also be corrosion resistant or at least capable of being coated with an anticorrosion component. Suitable materials that are often employed include a high-strength grade of copper-beryllium and steel.
Optical cables 1301 and 1302 enter the repeater 100 through the end caps 1201 and 1202, respectively. Optical cables 1301 and 1302 include an electrical conductor for supplying electrical power to the electrical components located in the repeater 100. The electrical conductors in the optical cables are in electrical communication with the respective end caps 1201 and 1202. In order to drop power to the electrical components a voltage must be established between the end caps 1201 and 1202. To accomplish the necessary voltage drop, electrical continuity must be interrupted between the end caps 120. Accordingly, some provision for interrupting electrical continuity needs to be provided since the housing 110 is generally formed from a metallic material.
Unfortunately, changing the material from which the housing 110 is formed from a conductive to a dielectric material is problematic because of the substantial structural and thermal demands placed on it. Not only must be the housing 110 be formed from a material strong enough to withstand the hydrostatic pressures of the undersea environment, but it must also be sufficiently thermally conductive to dissipate the waste heat generated by the electrical components within it. Very few available materials can provide the strength needed in such a small volume with the required thermal conductivity. Moreover, most materials that can provide the required strength and thermal conductivity are also good electrical conductors since thermal and electrical conductivity usually go hand in hand because they both arise from the mobility of electrons within the material).
Accordingly, it would be desirable to provide a pressure vessel for an undersea optical repeater that meets the stringent structural, thermal and electrical properties that such a pressure vessel requires.